Interpretive Summary: Histones are DNA-binding proteins. Modification of histones by the vitamin, biotin can cause changes in gene expression. The enzyme holocarboxylase synthetase is thought to add biotin to histones in eukaryotic cells. In this study, we evaluated a bacterial counterpart of eukaryotic holocarboxylase synthetase, Bir A ligase for biotinylation of various substrates. Data from this study will be used to understand the potential substrate requirements for biotinylation by this class of enzymes.

Technical Abstract:
BirA ligase, a prokaryotic ortholog of human holocarboxylase synthetase (HCS), is known to biotinylate proteins. Here, we tested the hypothesis that BirA ligase may also catalyze biotinylation of eukaryotic histones. If so, this would render recombinant BirA ligase a useful surrogate for HCS in studies of histone biotinylation. Biological activity of recombinant BirA ligase was confirmed by enzymatic biotinylation of the polypeptide p67, a known target of BirA ligase. Importantly, BirA ligase biotinylated both calf thymus histone H1 and human bulk histone extracts. Incubation of recombinant BirA ligase with H3-based synthetic peptides and cofactors revealed that lysines 4, 9, 18, and 23 in human histone H3 are targets for biotinylation by BirA ligase. Modifications of peptides (e.g., serine phosphorylation) affected subsequent biotinylation by BirA ligase, suggesting crosstalk among modifications. In conclusion, this study suggests that prokaryotic BirA ligase is a promiscuous enzyme and biotinylates eukaryotic histones; biotinylation of histones by BirA ligase is consistent with the proposed role of human HCS in chromatin structure.